1. Field of the Invention
The present invention pertains to the field of ammunition and explosives. More particularly, the invention pertains to the field of arming devices of the blocking or interrupting type which may be operated by fluid pressure or inertia.
2. Description of the Related Art
Safe and arm devices typically have an explosive train including an element which is displaced from the train to place the device in a safe condition and which is inserted into the trail to place the device in an armed condition. The element is, typically, a pellet of explosive mounted in a rotor or slide which is motivated, when conditions are appropriate for arming, to carry the pellet&. into the train. Since detonation of an explosive typically requires that it be subjected to a shock wave, as from a previously detonated explosive in an explosive train, it is known to provide a safe condition by providing a void in the train, the void being filled by some inert, but shock wave transmitting, material to establish an armed condition.
For safety, economy in construction, and reliability, it is highly desirable that insertion of an element for arming be motivated directly by an environmental condition only existing when arming is required. A typical example is the motivation of a element, such as an above-mentioned slide or rotor, by the inertia of the element when a projectile is fired from a gun. However, direct motivation of such an element may not be practical when the envirormental condition, such as mild acceleration or a relatively slight pressure change, provides relatively limited force. Although such a lack of force may be overcome by using low friction elements, by using energy stored in springs or batteries, by using electronic sensors and amplifiers, or by using very large inertia or pressure responsive elements, the resulting bulk, expense, and fragility are highly undesirable. Also, it is evident that a safe and arm device actuated by a relatively small environmental change or by stored energy is impracticably dangerous unless stringent precautions are taken to prevent premature arming when a similar change occurs during shipping, handling, or as a result of accident. Even where relatively large environmental forces are available, as from ram air in an air launched missile, safe and arm devices typically sense conditions for arming and assume an armed condition using mechanical or electromechanical devices which are relatively complex and, therefore, are expensive and unreliable and require further complexities to prevent improper arming.
It is known in an underwater ordnance device such as a mine to have an explosive train interrupted by a void and to arm the device by filling the void with water for transmission of a detonation shock wave, the filling typically occurring by gravity when water soluble plugs on the device exterior dissolve subsequent to placement of the device in its intended environment. In such underwater devices, it is apparent that large explosive train elements may be provided to generate a shock wave effective to initiate further detonation despite attenuation by the water, that a substantial length of time is available for dissolving the plugs and filling the void, and that this delay and the use of plugs soluble only in the intended environment provide stringent safety precautions. It is also apparent that such an arrangement using an inert liquid, while practical for underwater ordnance, is impractical in a safe and arm device for use, for example in an air launched missile, where bulk and weight must be minimized and arming must occur in a fraction of a second, or where, as in free-fall ordnance, there is no environmental condition change as substantial and enduring as that from air to undersea emplacement.